Recombinant Mouse Probable G-protein coupled receptor 128 (Gpr128)

What is the tissue expression profile of Gpr128 in mice?

Gpr128 exhibits a highly specific expression pattern in mice. Studies using semi-quantitative reverse transcription-PCR and Northern blotting have demonstrated that Gpr128 mRNA is highly and exclusively detected in intestinal tissues . This restricted expression pattern suggests that Gpr128 likely plays a specialized role in intestinal physiology. Researchers investigating this receptor should therefore focus their experimental design primarily on intestinal tissues and related functions.

What are the key structural domains of mouse Gpr128 protein?

Mouse Gpr128 contains two critical structural domains characteristic of adhesion G-protein coupled receptors:

• GPS (GPCR proteolysis site) domain - encoded by exons 10-12

• 7TM (seven-transmembrane) domain - partially encoded by exons 10-12

These domains are functionally significant, as targeted deletion of exons 10-12 (which encode the GPS domain and a portion of the 7TM domain) generates a complete loss-of-function allele through an out-of-frame reading frame shift . The GPS domain typically mediates proteolytic processing that is important for receptor maturation and function in this class of receptors.

What are the molecular characteristics of mouse Gpr128?

The molecular details of mouse Gpr128 are well-documented in genomic databases:

These reference identifiers provide access to sequence information and predicted structural features that can inform experimental design and genetic manipulation strategies .

How is recombinant mouse Gpr128 typically produced and what are its specifications?

Recombinant mouse Gpr128 for research applications is typically produced with the following specifications:

Production typically involves expression of either full-length or partial-length protein in mammalian cell systems to ensure proper folding and post-translational modifications essential for receptor functionality .

What considerations should be taken into account when designing experiments with recombinant Gpr128?

When designing experiments using recombinant Gpr128, researchers should consider:

• Protein stability - Gpr128 is stored in PBS buffer, suggesting this provides optimal stability. Avoid repeated freeze-thaw cycles which may compromise protein integrity.

• Expression system compatibility - Since the native protein is produced in mammalian systems , experimental designs should account for potential differences in post-translational modifications when using different expression systems.

• Purification tag influence - The His-tag used for purification may influence protein-protein interactions in some experimental contexts and should be considered when interpreting binding assays.

• Lead time requirements - Custom production requires 5-9 weeks lead time , which should be factored into experimental timelines.

• Physiological relevance - Given Gpr128's intestinal specificity, experimental conditions should mimic intestinal physiology where possible.

What phenotypic changes are observed in Gpr128 knockout mice?

Targeted deletion of Gpr128 in mice results in several notable phenotypic changes:

• Reduced body weight gain - Beginning at 24 weeks of age, Gpr128^(-/-) mice exhibit significantly lower body weight (25.74 ± 4.50 g) compared to wild-type mice (30.81 ± 2.84 g) (n = 10, P < 0.01) .

• Altered intestinal motility - Knockout mice display increased frequency of peristaltic contractions in the small intestine (detailed in section 3.2) .

• Normal development - Heterozygous (Gpr128^(+/-)) mice show normal development and fertility, indicating that the targeted locus does not have detrimental dominant activity .

These phenotypic changes suggest that Gpr128 plays a regulatory role in body weight homeostasis and intestinal motility, making it a potential target for metabolic and gastrointestinal research.

How does Gpr128 deletion affect intestinal motility?

Gpr128 deletion significantly alters intestinal motor function. Quantitative analysis using the Trendelenburg preparation revealed:

At 8 weeks of age:

At 32 weeks of age:

Additionally, the frequency of slow wave potential in Gpr128^(-/-) intestine (approximately 36-37/min across different intraluminal pressures) was also higher than in wild-type intestine .

These findings suggest that Gpr128 functions as a negative regulator of intestinal contractility, and its absence leads to increased intestinal motility across different ages and pressure conditions.

How can researchers generate and validate Gpr128 knockout models?

The generation of Gpr128 knockout models involves several methodological steps:

• Targeting vector construction:

  • Use bacterial artificial chromosome (BAC) retrieval methods

  • The BAC clone bMQ-239c21 from the 129/Sv strain served as the source material

  • Replace exons 10-12 (encoding the GPS domain and part of the 7TM domain) with a PGK-Neo cassette

  • Include 7.1 kb of homologous DNA upstream and 5.3 kb downstream as recombination arms

• Embryonic stem (ES) cell electroporation:

  • Electroporate linearized targeting vector into ES cells derived from 129/Sv mice

  • Select G418 and GANC-resistant clones

  • Verify recombination using PCR with specific primer pairs:

    • Forward primer P1: 5'-CCATAGGAAGAATAATATCAACCAATC-3'

    • Reverse primer P2: 5'-CTGAGCCCAGAAAGCGAAGGA-3'

    • Forward primer P3: 5'-ACAAAAGCAAAACAAGGTCTGGAAAG-3'

    • Reverse primer P4: 5'-CCTCCCCCGTGCCTTCCTTGAC-3'

• Validation strategies:

  • Genotyping: PCR analysis of genomic tail DNA

  • Expression analysis: Semi-quantitative RT-PCR and Northern blotting

  • Protein detection: Immunofluorescence staining

  • Functional validation: Assessment of intestinal motility using the Trendelenburg preparation

This methodology provides a comprehensive framework for researchers seeking to generate their own Gpr128 knockout models for functional studies.

What techniques are effective for measuring intestinal motility in Gpr128 research?

The Trendelenburg preparation has proven effective for studying intestinal motility in Gpr128 research. This method involves:

• Preparation of intestinal segments from mice at different ages (8 and 32 weeks)

• Application of varying intraluminal pressures (1, 2, and 3 cmH₂O)

• Simultaneous recording of:

  • Peristaltic contractions (measured as frequency per 15-minute interval)

  • Extracellular electrical potential from the gut wall to measure slow wave frequency

This approach allows for quantitative assessment of both mechanical and electrical aspects of intestinal motility, enabling detailed characterization of the effects of Gpr128 deletion on gastrointestinal function.

What are the challenges in interpreting functional data from Gpr128 studies?

Researchers should be aware of several challenges when interpreting data from Gpr128 functional studies:

• Tissue specificity - Given that Gpr128 is exclusively expressed in intestinal tissues , findings from non-intestinal tissues or generalized systems may not accurately reflect Gpr128's physiological role.

• Age-dependent effects - The intestinal motility phenotype shows some variation between 8-week and 32-week-old mice , suggesting that age is an important variable in Gpr128 function.

• Genetic background effects - The Gpr128 knockout model was generated on a mixed 129/BL6 background , which could introduce variability due to strain-specific genetic modifiers.

• Unknown ligand - Prior to these studies, "there was little information regarding the ligand or the physiological function of GPR128 in mammals" , and this knowledge gap persists. Without identified ligands, interpreting receptor function remains challenging.

• Technical variability - Different methods for assessing intestinal function may yield varying results, necessitating standardized approaches for cross-study comparisons.

What are potential research directions for further understanding Gpr128 function?

Based on current knowledge, promising research directions include:

• Ligand identification - Developing screening assays to identify endogenous ligands for Gpr128 would significantly advance understanding of its activation mechanisms.

• Signaling pathway elucidation - Characterizing the downstream signaling events following Gpr128 activation would clarify its molecular mechanism of action.

• Cell-specific deletion models - Generating conditional knockout models with intestinal cell-type specificity could pinpoint which intestinal cell populations mediate Gpr128's effects.

• Metabolic pathway investigations - Given the reduced weight gain phenotype in knockout mice, exploration of how Gpr128 influences metabolic pathways could reveal novel connections between intestinal function and systemic metabolism.

• Translational potential - Investigating whether Gpr128 modulators could serve as therapeutic targets for gastrointestinal motility disorders or weight management.